Bioelectricity, which refers to an ultra-fine biomedical signal flowing through the human body, is a signal of the shape of current or voltage generated from a nerve cell or a muscular cell. The bioelectricity is classified into ElectroCardioGram (ECG), ElectroMyoGram (EMG), ElectroOculoGram (EOG), ElectroEncephaloGram (EEG), and so forth. The source of the bioelectricity is a membrane potential, which is stimulated to produce an action potential under predetermined conditions. The measurement of the action potential in a single cell is achieved by a special fine electrode, and this action potential is the source of a bioelectric potential.
The measurement of the action potential in a larger unit is achieved by a surface electrode. In this case, an electric field generated due to the action of many cells distributed around the electrode is measured. Electrical conduction in a living matter is achieved by ions, but electrical conduction in a measurement system is achieved by electrons, thereby requiring an electrode.
Among biomedical signals, particularly, variation in a potential of a brain wave signal generated from the scalp of a human body is approximately 10˜100 μV. The biomedical signal having above size is weak so that this signal cannot be detected by the human body. However, the biomedical signal, which is abnormal, is bad for health of the human body, such as the lowering of the function of the human body and the generation of disease, and is dangerous. Thus, it is important to maintain the normal state of the biomedical signal. Further, biomedical signals are used as data for clinical diagnosis in the medical field. For example, biomedical signals are sources for diagnosing a reagent's illness by means of a non-invasive method, and are essential in clinical examination.
When the above biomedical signal is measured, an electrode of a sensor module is attached to the skin of the human body. The electrode, which is attached to the skin, is the most essential element of the sensor module. Generally, in order to sense an electric signal, the electrode is made of a conductor, through which current flows. Further, in order to improve conductibility, the electrode is made of conductive material made of gold (Au) or silver (Ag).
FIGS. 9A and 9B are perspective and sectional views of a conventional electrode for measurement of bioelectricity. The conventional electrode for measurement of bioelectricity is made of metal and has a disk shape. That is, the conventional electrode for measurement of bioelectricity comprises a base 3 formed in the shape of a foam pad, a fabric, a nonwoven fabric, or a tape including synthetic polymer and natural polymer, and provided with an acryl-grouped biocompatible adhesion paste deposited on one surface thereof; a stiffener 2 made of polymer and attached to the other surface of the case 3 for preventing evaporation of moisture; a snap 1 made of brass and installed at the central portion of the stiffener 2, and an electrode element 4 made of plastic reinforced with glass fiber and deposited with silver/silver chloride, the snap 1 and the electrode element 4 being fixed to each other; a conductive hydro gel adhesive agent 5 coating the exposed surface of the electrode element 4; and a release film 6 attached to the hydro gel adhesive agent 5 and the remaining adhesion paste on the base 3 for protecting the hydro gel adhesive agent 5 and the remaining adhesion paste on the base 3.
The above conventional electrode for measurement of bioelectricity uses a conductive adhesion gel for attaching an electrode element, such as the scalp electrode, to the skin. In the case that the conventional electrode uses the conductive adhesion gel, a long preparation time is required. Further, the conductive adhesion gel supplies unpleasantness or discomfort to a reagent due to its own viscosity. In order to obtain more precise measurement results, before the conductive adhesion gel is applied to the scalp of the regent, the scalp is slightly rubbed. Such an action generates damage to the scalp, thus being not preferable. It is a well-known fact by the research of brain that the damage to the scalp increases the danger of infection of a virus transmitted through blood, such as Human Immunodeficiency Virus (HIV), Hepatitis C Virus (HCV), or Creutzfeldt-Jacob Disease (CJD).
The biomedical signal measured by the electrode element is applied to an electronic circuit for processing the signal through a wire (not shown) having a length of several meters. Here, in the case that the biomedical signal to be measured is EEG, the level of the signal is excessively fine, i.e., several tens of μV. Accordingly, when the wire is not shielded, there is an ample probability of that the discrimination of the signal is rapidly deteriorated due to a noise component such as interference of power of 60 Hz. That is, a biomedical signal having a fine level is transmitted to an amplification circuit through the wire having a comparatively long length so that the biomedical signal is amplified by the amplification circuit. Here, the biomedical signal may be attenuated by the wire. Further, in the case that the biomedical signal is interfered by external noise, the amplification circuit amplifies the external noise as well as the biomedical signal. Although an electronic circuit, such as a high or low band-pass filter, is prepared to filter the signal, the noise components, which were already introduced into the signal during the signal transmission, are not completely eliminated and are measured/analyzed together with the biomedical signal.
In order to solve the above problems, many methods have been proposed. In one method, the interference due to noise of 60 Hz is reduced through a shielded wire. However, the above method still has drawbacks, such as loss of the signal due to the length of the wire and interference by a magnetic phenomenon due to a loop of the long wire, thus being disadvantageous in terms of noise characteristics, reliability in measurement, or costs.